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Author Topic: The Beast of Turin  (Read 1711 times)

Adrian

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The Beast of Turin
« on: 18 November 2020, 11:25:43 am »
Rhys and I are building ‘The Beast of Turin’.  I know what your thinking ‘Are they trying to build the biggest cyclekart on Earth’?
Using one of the many side views available on-line and a side elevation plan (also on-line) I enlarged the side elevation drawing so that the wheels were 24” in diameter, the O/D of the 17” Honda wheels.
What resulted was a surprise, the wheelbase was just 66” so we could get a fairly scale like appearance, in proportion to the wheels, the originals being very narrow too.
OK, it's a bit tall, but sitting in a wooden tub bolted to the inside of the chassis rails you should just about see over the bonnet. It looks a real character!
Unlike my GP Renault this one was going to be very simple. (apart from the fact that its chain driven and we want the outside sprocket and chains on show).
Handling is the primary focus of our attention, in particular accuracy of steering. No more under-steer and easily induced and controllable over-steer when it’s wanted are our main aims. Smooth and controlled drifting around the bends is what we are after, both on and off the tarmac. 7.5hp is not a lot but we might tweak that up to ten or 12.
Engine and transmission are going to be very important. Acceleration, instant response to throttle and a competative top speed are the goals.  Thanks for the offer Anton but we won’t need the Nitrus Oxide. (just joking).
We are trying a new basic chassis design using much lighter (20 X 60 X 1.5 RHS and three 35mm diameter round tube section cross members.
Six mm ply will form the tub and all the bulkheads with as much material removed as possible to maintain the shape and rigidity. Body panels will be very thin aluminium sheet and the tail cone will be plank on frame like model boats hulls.
Actually, I started drawing this up ages ago and unlike with the Renault, I will be keeping this thread up to date with lots of piccies and all my drawings and our thought-processes in the design and build.
I will include the bits where you make it up as you go along too. We’ve had some of that already of course.
Right then! Off we jolly well go.

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Marek.Z.N

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Re: The Beast of Turin
« Reply #1 on: 18 November 2020, 04:22:42 pm »
great kart to make. should look great. its such a recognisable and different shape to all the others. with power whats wrong with 7.5 buff horses, follow Collin Chapman's advise of just add lightness and we have seen that gets you fast (as seen in Bill's, Jim's and Chris Slade's CKs). I would love to see the sketches of the design if you could put them up here

Adrian

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Re: The Beast of Turin
« Reply #2 on: 19 November 2020, 04:16:48 pm »
It will be very light.
It will have the right choice of tyres.
It will be softly spring (on the front only of course).
It will have GoKart type steering.
It has a 66" wheelbase.
it has a 36" track.
It uses 17" wheels
It has a slightly tweaked GX200 Honda engine.
It has a Comet T/C.

All pretty standard stuff so why do CK's all handle so differently? How can you make sure that the CK you are building will handle as you want it to?

I hope the following prompts the old (and the sixteen year old) grey matter into action.

For me, handling comes down to how the CK behaves as it enters a corner, what happens whilst it goes round the corner and how it exits the corner.

Some of the handling characteristics come down to the centre of the roll axis being on the axle line (because of the two beam axles). Nothing you can do about that but the centre of gravity can be played with. It can be moved fore and aft and above or below the roll axis. If the C of G is below the roll axis it will help to prevent the car rolling (obviously) whereas if the C of G is above the roll axis it will have the opposite affect and cause the CK to roll towards the outside of a corner.
The effect of reducing the roll is to reduce the weight being transferred to the outside wheels or to put it another way, maintaining as much weight as possible on the inside wheel. Assuming both rear wheels are driven then this will tend to increase the overall grip of the rear tyres and as as result, induce understeer.
With the C of G above the roll centre weight is transferred from the inside tyre to the outside tyre reducing the grip of the inside tyre. The overall grip of the rear wheels is now reduced inducing oversteer. Grip of the inside rear tyre is also reduced since it is now spinning relative to the ground. (More on time-dilation later).

Moving the C of G forwards and backwards plays a big role too. With the driver sitting as far back as possible (which is what we do) and the engine and transmission being at the back  there is more grip from the rear tyres than there is from the front tyres.

Cornering is induced by the front wheels steering to the left or right but they have a tough time of it because there is more grip from the rear tyres due to the greater weight being carried by them and in addition, there is the solid, unsuspended rear drive axle to consider. The result .....understeer.

Inevitably the driver will attempt to get round the corner by inducing oversteer. Foot down and grabbing a big handful of lock will hopefully bring the back end swinging out due to lack of grip and the pendulum effect. Then the car rolls more, because of the front axle being suspended and the flex in the rear tyres. The rest is largely down to the driver who just might keep the arse out and apply opposite lock when suddenly. the back end grips and your off down the straight again.
Phew, that's really fun and often spectacular but it's not fast.

I should mention that steering geometry is also of course very important.
Golden Rules are;
Caster is a must
King-pin inclination is a must
Correct Ackerman is a must
Camber is important because when with the caster angle and king-pin inclination is set correctly the CK is easier to control when in an opposite lock condition and oversteer is easier to achieve.
Correct Tracking is Vital.
A front anti-roll-bar is helpful.

I will try to get the drawing of the beast up later today.

Some of you may disagree and have you own ideas of Understeer, what causes it and how to minimise it? If you have, please post them. If I havn't covered it here I would be pleased to have your thoughts on the matter and hopefully this posting may help future builders to consider these matters and get to understand them

Adrian

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Re: The Beast of Turin
« Reply #3 on: 19 November 2020, 04:25:18 pm »
Hopefully a plan is attached.

sjc56

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Re: The Beast of Turin
« Reply #4 on: 19 November 2020, 06:36:28 pm »
Hi,
 As this is new to me, out off interest what would a typical Ck weigh.
Also do you happen to know what two steel chassis rails weigh.
Thanks
Stuart

jim

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Re: The Beast of Turin
« Reply #5 on: 19 November 2020, 08:06:46 pm »
I like the idea of having the drive chain and brake disc on the outside which will mean you can get your body closer to the axle. its gonna look fantastic.

Adrian

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Re: The Beast of Turin
« Reply #6 on: 21 November 2020, 02:03:55 pm »
Does nobody have any ideas on improving steering?
I think tyres play a major role here.
Narrow, flexible tyres have been suggested and narrowing the back axle and fitting soft front springs too.

I think the heaviest item going in the CK is the driver and he/she is right at the back with the other heavy bits.
Looking at my drawing what do you think the weight distribution might be? say the cart is going to weigh 100kg and I am 85kg.
The weight distribution of the chassis with engine etc and front axle and steering probably makes it 60:40 in favour of the back end. Legs are heavy and most of them will be forward of the C of G but the rest of me is behind it so again say 60:40 in favour of the back?
The soft front spring will keep both front tyres on the road while the inside wheel on the rear axle will un-weight itself.
Assuming the tyre grip is proportional to the weight distribution then the front end will need tyres that stick much better than the rears to avoid understeer because the front end is so much lighter than the back. I haven't put that very well, have I? I think I might mean that you need to blow the rear tyres up a lot more than the fronts and have less rubber in contact with the ground on the rears.

Some of us have very nobbly tyres and fitting those on the back with smoother treaded fronts might help too?

I'm on my laptop just now but if I can access the files on my workshop PC I will post some more images of the design iterations of the Beast.
The first one compares the fitment of 14" and 17 " wheels. The 14" ones are too small really but help capture the character. Anyway, we are going with the 17's.
The next one is my favourite idea. A total cartoon of a car with lots of beastie about it.
We'll see??

ChrisS

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Re: The Beast of Turin
« Reply #7 on: 21 November 2020, 06:19:57 pm »
Hi,
 As this is new to me, out off interest what would a typical Ck weigh.
Also do you happen to know what two steel chassis rails weigh.
Thanks
Stuart
Hi Stuart, mine weighs in at 105kg and the ratio is 33% front 66% rear - ck only, no driver. If you look at the 'stability' thread on this forum you might find more.  Regarding your chassis rails, if you google the section you can find the kg/m.

Marek.Z.N

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Re: The Beast of Turin
« Reply #8 on: 22 November 2020, 04:36:10 pm »
If the plan is to have your body above the rear axle and the engine behind you then your weight distribution will be extremely bias to the back and that wont help with cornering. having the weight as far forward as possible while keeping it looking good will keep traction and having most of the mass nearer the centre rather than that far back would reduce the angular momentum meaning it would turn faster. hope that might help :)

sjc56

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Re: The Beast of Turin
« Reply #9 on: 22 November 2020, 06:58:24 pm »
Hi, how to improve the steering, I’m new to cyclekarts so I don’t want to come over as a know it all, so here goes.

I reckon if you narrow the rear track it would make steering worse. This is because if you move the rear in it will gain grip, if you move out it will lose grip, same applies to the front. By moving the rear in you have effectively made the front wider in relation to the back, therefore losing grip on the front. Grip and stability are two different things, I’ll try to explain why you gain grip by moving wheels in. Imagine the axle as A horizontal axis then from the centre of that imagine a vertical axis. Now put yourself in the seat to create weight that would move to the outside of a corner, centrifugal force does this. Now imagine all this as a simple ‘L’ shaped lever with the turning moment where the vertical axis meets the horizontal axis, as you move the wheel further away from the centre point, less weight would be applied to the tyres contact patch therefore less grip on the tarmac.
With this in mind the front has a relationship with the rear. There are other factors that should be taken into account, but hopefully this might help.

Chris Brown

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Re: The Beast of Turin
« Reply #10 on: 23 November 2020, 10:46:28 am »
That's very interesting, might explain why my kart seems to need more lock to turn than others. Being a Morgan it's rear track is as narrow as it's possible to get, ie 0, being a single rear wheel.  ;)

StefanN

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Re: The Beast of Turin
« Reply #11 on: 14 December 2020, 09:28:22 am »
Thought you'd enjoy Stefan Marjoram's drawing Adrian.


Adrian

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Re: The Beast of Turin
« Reply #12 on: 21 December 2020, 04:11:46 pm »
Thanks Stephan
I love that guys drawings.
I must get some of my cartoons sorted.